In recent years motor vehicles have become increasingly more powerful and capable of traveling at higher and higher speeds. Speed limits have also been increasing and often vehicles travel considerably beyond posted speed limits. These powerful automobiles are so well built that high speeds can be attained without the driver being aware of just how fast he or she is traveling.
The availability of cruise control devices have made it easier to stay within acceptable speed limits, but many drivers fail to take advantage of such devices making it necessary that the driver constantly look at the speedometer in order to maintain proper speed. The more often the driver's eyes are taken away from the road, the greater the chance of getting into a problem situation. A peripherally viewed speed indicator, one that lessens the need for the driver to look away from the road, would provide an enhanced safety factor to current speedometer technology.
There have been some attempts to color code the speedometer to make the driver more aware of changes in speed, but these have involved some complex and clumsy mechanisms and did not really achieve the desired result.
Hills, in U.S. Pat. No. 2,286,737, discloses a speedometer having a plate with the speed numbers on its face. Behind the plate are two opposingly situated light bulbs and a Lucite rod that rotates between them. A pointer situated in front of the plate rotates with the rod. Between the Lucite rod and the plate is a disc divided into three colored areas, green, amber and red. As light is transmitted from behind the speedometer face it passes through one of the colored areas causing colored light to be transmitted through an opening in the hub to the pointer. The light is green for speeds from 0 to 30 mph, amber for speeds from 30 to 50 mph and red for speeds above 50 mph. The mechanisms in this speedometer would be cumbersome and impractical by modern standards. A similar device using the same colors for like speed ranges is disclosed by Dickson et al. in U.S. Pat. No. 2,287,605. The round transparent face of the speedometer dial has lines and numerals etched into the rear of the dial. The depressions are filled in with a light reflecting substance. An annular member located behind the face and within a central hub is divided into three segments, one each of the three colors noted above. A rear light source and an optical system transmit appropriately colored light to the pointer in front of the face and for edge illumination to the center portion of the dial. The colors change as the speed changes. In the speedometer of Christensen (U.S. Pat. No. 2,314,817) it is only the pointer that is illuminated in one of the three colors, green, amber and red. A color screen is lit from behind and the colored light directed through a slot to the pointer. When the speed is between 0 and 30 mph the pointer takes on a green color, 30 to 50 mph an amber color, and above 50 mph, a red color.
The speedometer of Zargarpur (U.S. Pat. No. 2,907,297) also uses three colors to indicate the speeds, green 0 to 25 mph, amber 25 to 50 mph, and red above 50 mph. The speeds are registered on a linear scale. There is a slot below the scale and a rotating drum behind the slot. The drum has a red section and a black section separated by a waved line. A color disc is situated at one end of the drum. Light shines through the color disc and onto the drum. The rotating areas cause the colored light showing through the slot to be seen in light to dark hues of the three colors.
In U.S. Pat. No. 4,935,850, Smith, Jr. teaches a speedometer that utilizes three semicircular plates spaced apart along a shaft. A pointer is situated in front of the forward plate. The pointer and center plate are rotated by the shaft which is activated by the speedometer servo-driver. The front plate has an outer arc with speed numerals and indicator lines which are made up of fiber optic bundles that transmit ambient light to the rear. The center plate has a non-reflective mid-portion and an outer reflective arc and the rear plate has a black center and transparent arc containing a series of monochromatic filters. Bulbs behind the rear plate shine light through the colored filters. As the center plate rotates different colors are transmitted and reflected back through the fiber optic bundles to color the numerals and speed indicator lines. The light is white for speeds from 0 to 25 mph, blue for speeds form 25 to 45 mph, yellow for speeds from 45 to 65 mph, and red for speeds over 65 mph.
All of the prior art speedometers that exhibit colors to highlight specific speeds utilize color transmission systems where the colors are located behind the speedometer face and must be transmitted by different optical means to the pointer, hub area, or the numerals and speed indicator lines. There is a need for a simple system that utilizes colors to indicate different speeds in such a manner that the driver can observe the colors peripherally without having to constantly look at the speedometer. There is a need for such a system where the colors are more visually prominent, more colors can be used, and complex optical and light transmission mechanisms are not necessary.